Thermoplastic elastomers (TPEs) are materials that have rubber elasticity at room temperature like vulcanized rubbers and can be injection molded at high temperature like plastic materials. That is, thermoplastic elastomers are intermediate materials between rubbers and plastics.
Due to such characteristics, thermoplastic elastomers can be used in various applications where ductility is required, including sporting goods, food packages, medical devices, portable IT external devices, and home appliances. In addition, thermoplastic elastomers can be injection molded into articles, which are impossible to produce from vulcanized rubbers, in a short time. Furthermore, thermoplastic elastomers can also be recycled and thus cause no environmental problems, unlike vulcanized rubbers.
In recent years, attempts have been made to use thermoplastic elastomers (TPEs) as materials for door diaphragms of washing machines and dryers. Such a diaphragm is illustrated in FIG. 1. The diaphragm 10 is a member disposed between a door and a water tank of a washing machine. The diaphragm is required to have a function to absorb impact and vibration while preventing water stored in the water tank from leaking toward the door.
Thermosetting resins have been used as materials for diaphragms. Such materials are susceptible to abrasion and are impossible to recycle. Thermoplastic elastomers as materials for diaphragms should have a surface hardness (Shore A) of 50 A or less. Such low hardness enables thermoplastic elastomers to absorb vibration from motors and reduce noise during operation.
However, thermoplastic elastomers having a surface hardness (Shore A) of 50 A or less exhibit poor physical properties (such as elongation permanent set) at high temperatures compared to vulcanized rubbers, which limits their application range.
In attempts to overcome such limitations, thermoplastic elastomers have been alloyed with other resins. However, the alloys have thus far failed to provide satisfactory thermal properties at high temperatures and even lose surface ductility, which is one of the inherent advantages of thermoplastic elastomers.
U.S. Patent Publication No. 2005-0288393 discloses a thermoplastic elastomer composition including a thermoplastic resin, a block copolymer, a core-shell copolymer, and an oil. However, the composition is not suitable for use in electrical/electronic parts, particularly, diaphragms for washing machines, due to its surface hardness (Shore A) exceeding 70.
U.S. Patent Publication No. 2004-0151933 discloses a thermoplastic elastomer composition including a thermoplastic resin, a rubbery elastomer, a saturated elastomer, and an oil. However, the surface hardness (Shore A) of the thermoplastic elastomer composition cannot be maintained at 50 A or less, which limits the use of the composition.